Interpretive Summary: The fungus named Aspergillus flavus produces a poison called aflatoxin when it infects corn kernels. Aflatoxin prevents the corn from being used commercially. The best strategy for controlling this problem is to develop corn that is resistant to aflatoxin contamination, through the expression of different resistance traits. We screened 36 genetically-different African lines of corn, using a laboratory kernel screening test, and found that one-third of the lines were as resistant as our best lines. These lines appear to resist toxin production by inhibiting fungal growth, and also possess great variation in protein expression. This information suggests that we may be able to double the number of lines currently in U.S. breeding programs for aflatoxin-resistance. Also, we may be able to identify resistance traits different from those already known. This could lead to a more rapid development of commercially-useful, resistant lines of fcorn, and to future savings of millions of dollars to growers, as a result of the elimination of aflatoxin contamination of corn.

Technical Abstract:
Thirty-six inbred lines selected in the savanna and midaltitude ecological zones of West and Central Africa for moderate to high resistance to maize ear rot under severe natural infection were screened using the kernel screening laboratory assay (KSA) for potential resistance to aflatoxin contamination. Results of screening tests showed that about one-third of the inbreds accumulated aflatoxins at levels as low as or lower than promising genotypes, GT-MAS:gk or MI82. Growth of Aspergillus flavus was quantitated in 10 selected inbreds of the 36, six potentially resistant and 4 susceptible, using an A. flavus transformant containing a GUS reporter gene linked to a B-tubulin gene promoter in conjunction with the KSA. A positive relationship between levels of aflatoxins accumulated and growth of the fungus was demonstrated in the majority of genotypes, however, one resistant inbred supported a high level of fungal infection but low aflatoxin levels, possibly indicating the presence of aflatoxin pathway inhibitors. Kernel proteins of these same 10 lines were then separated using SDS-PAGE. Comparisons of protein profiles among African lines and between them and resistant and susceptible controls demonstrate greater protein diversity among the African genotypes than between the resistant and susceptible controls. Field evaluation of potentially resistant inbreds may significantly broaden the resistant germplasm base against aflatoxin contamination. Biochemical resistance markers different from those being identified and characterized in "domestic" genotypes may also be identified in the African lines. These discoveries could significantly enhance the host resistance strategy of pyramiding different traits into agronomically-useful maize germplasm.